Tolerance And Accumulation Characteristics Of Copper In Melissa Officinalis

In recent years,the soil pollution was become a worldwide problem,remediation of the polluted soil is one of the most important topics in the field of environmental protection in China.The traditional methods with physical and chemical technologies may consume not only the more time but also more power.Furthermore,those methods will produce secondary pollution potentially.Therefore,the phytoremediation as a more suitable technology has widely prospect in application.The phytoremediation of heavy metals has become one of the hotspots in the field of soil remediation.The mechanism of copper tolerance were explored by using Chlorophyll,antioxidant enzymes,soluble protein?SP?,malondialdehyde?MDA?,the content of Cu²⁺and ultra-structural analysis in Melissa officinalis by the methods of transmission electron microscope,flame atomic absorption spectrophotometer and physiological and biochemical measurement.Different Cu²⁺concentrations(0,200,400,800 and 1000 mg·kg^-1)were chosen for 28 days test.This study focuses on the mechanism of tolerance and accumulation of Melissa officinalis,and the feasibility of Melissa officinalis as a phytoremediation plant.The main results in this work are summarized as follows:?1?The concentration of Cu²⁺was positive correlation with copper treatment concentration;the total Cu²⁺concentration in plants reached up peak at 400 mg·kg^-1?0.71 mg each pot?then decline;throughout the experiments,these indexes of tolerance?the bio-concentration factors and the translocation factor of Melissa officinalis were shown a decline trend,the minimum value of them were 0.53?1.01?0.10 respectively;The concentration of copper in aboveground was greater than underground;the biomass of Melissa officinalis was shown tended to promote weakly and inhibited strongly with the increasing Cu²⁺concentration.?2?Activities of antioxidative enzymes1)At the same Cu²⁺treatment time,the SOD of Melissa officinalis were shown a significant increase at low doses yet an inhibitory at high doses,the peak value of SOD was appeared at 400mg·kg^-1,the decreasing trend was shown when the Cu²⁺concentration more than 400 mg·kg^-1.At the same Cu²⁺treatment concentration,with the increase of treatment time,the SOD was significant increase compared with CK groups of 200 mg·kg^-11 and 400 mg·kg^-11 at 14_thh day,the significant decrease was appeared at 21_thh day,the overall trend is increased at first and then dropped,at 1000 mg·kg^-1 groups,the SOD was decline in the whole process.2)At the same Cu²⁺treatment time,the GPX of Melissa officinalis were shown the increasing trend in the low does groups(200 mg·kg^-1 and 400 mg·kg^-1)with the Cu²⁺concentration,and then decreased briefly at 14_th day,after that,it was continued to increase.The peak value of GPX was appeared at 28d of 400 mg·kg^-1,The GPX of the 800 mg·kg^-1 group was increased with the increasing process time,the GPX in the 1000 mg·kg^-1 group was decreased at 28d.?3?MDA content and SP content1)The MDA content was increased with the increasing of Cu²⁺treatment concentration and the treatment time in the whole process,in addition to the 1000 mg·kg^-1 groups,it began to decline after 14^th.2)The content of SP in 200 mg·kg^-1 and 400 mg·kg^-11 groups were increased with the increasing treatment time at same Cu²⁺concentration,but the SP content of 800 mg·kg^-1 groups was began to stabilize after the temporarily reduce,the trend of steady decline with the increasing treatment time was shown at 1000 mg·kg^-1.Moreover,at the same treatment time,the SP content of Melissa officinalis was shown the trend that a significant increase at low doses yet an inhibitory at high doses.?3?Chlorophyll contentIn these groups under the same treatment times of copper,the variation trend of chlorophyll content in Melissa officinalis was shown increased in low copper concentration and decreased in high copper concentration.The chlorophyll a and b could be promoted when the Cu²⁺concentration were 200⁴00 mg·kg^-1,however,it was Inhibited at 800¹000 mg·kg^-1;On the other hand,at the same treatment concentration of Cu²⁺,the chlorophyll content of Melissa officinalis was constantly increased with increasing treatment time at 200⁴00 mg·kg^-1,the trend of first increased and then decreased was appeared at 800 mg·kg^-1,at 1000 mg·kg^-1,the chlorophyll content was steady decline.?4?The results of the ultrastructure showed that at the high Cu²⁺does,the chloroplast stepped construction of the leaves was damaged:hierarchical fuzzy,massive quantities of osmiophilic granules,plasmolysis and the rarefaction and vacuoles of the mitochondrial structure could be observed;the typical grana intergranal thylakoid structure was destroyed;the starch granules was decreased;density and concentration of cell wall were decline.There were a large number of black dense particles.The plasmolysis of the root tip cells was observed.The main binding sites of Cu²⁺were both on the cell wall.The results suggested that Melissa officinalis would be a potential plant for phytoremediation in Cu-contaminated soil.There were at least two ways contributed in the mechanisms of copper tolerance:1)Cu²⁺binding to cell wall is one of the major detoxification mechanisms;2)The regulation of its own antioxidant enzyme system is another way to alleviate the copper stress.